It is known to deposit a layer of material onto a base material (also known as an intermediate material). Such techniques are frequently used in the semiconductor industry to apply coatings or films. Problems can arise when the intermediate material is thin. Traditional deposition techniques can cause damage to the intermediate material because the energy of particles hitting the material's surface during deposition of the layer may cause damage to the intermediate material. Whilst thicker materials may only suffer surface damage, thin materials may suffer damage throughout most or all of its thickness.
Graphene is a flat monolayer of carbon atoms packed into a honeycomb lattice. Graphene has attracted considerable attention due to its peculiar and superior electronic, optical, thermal, mechanical properties characteristics. The important properties of graphene include high intrinsic charge carrier mobility and tunability of its properties by applying a gate voltage. The properties of graphene are at its best when graphene is pristine, i.e. absent of any damage. However, as graphene is only one monolayer of carbon atoms, the C—C bonds thereof are easily broken during deposition of layers thereon. Therefore, only thermal evaporation is known to be suitable for deposition of a layer onto graphene. This greatly limits the choice of materials or layers in graphene devices.
Sputter deposition is a method of depositing films by sputtering. Sputtering is a process whereby atoms are ejected from a solid source material (also known as a target material) due to bombardment of the source material by energetic plasma particles. The ejected atoms can be deposited on a surface of a workpiece to form a film thereon. Sputtering is a widely used technique in the hard-disk drive industry and in the spintronics and optoelectronics sector, for example, to form indium-tin-oxide coatings. However, sputtering is known to be unsuitable for depositing films onto graphene because the ejected atoms from the source material bombard the graphene with enough energy to cause disorder into graphene. This degrades the graphene and leads to it being non-pristine.